Many modern satellite systems include multiple satellites that communicate with each other in space. The communications link between the satellites is called a “crosslink.” Crosslinks can be implemented in many ways, including using radio frequency (RF) signals, or laser light. RF crosslinks can have wide beamwidths that provide for relatively easy signal acquisition and tracking, but the wide beamwidths also allow for relatively easy intercept. Laser crosslinks, on the other hand, have very narrow beams which protect against signal intercept, but increase the difficulty of signal acquisition and tracking.
Conventional laser crosslinks utilize optical devices to receive the laser light and to focus the laser light on one or more detectors in the focal plane of the optical devices. The optical devices are typically exposed to open space so that they can receive the laser light. The detectors are also exposed to space inasmuch as the location of the focal plane requires it.
Space presents a radiation and electromagnetic interference environment that is harsh on electronics, and laser light detectors typically include electronics that are particularly sensitive to radiation and electromagnetic interference. Shielding the detectors is difficult, in part because they are maintained in the focal plane of the exposed optical devices, and producing radiation-hardened detectors can be expensive.
Accordingly, a significant need exists for methods and apparatus for providing inexpensive, yet robust, laser crosslinks.